1) Field of the Disclosure
The disclosure relates to composite material compositions, coatings, and methods using segmented copolymers, and in particular, to composite material compositions, coatings, and methods using segmented copolymer elastomers and solid particulate fillers.
2) Description of Related Art
Elastomeric materials are required in a broad variety of applications, including use in low temperature, subfreezing environments, such as less than −50° C. Elastomeric materials that possess the ability to demonstrate a high degree of toughness through both high elongation and tensile strength find application in a variety of environments, such as the aerospace environment, where such low temperatures are common.
However, many known elastomers may not maintain their advantageous elastic properties at such low temperatures because such known elastomers may comprise polymer species that cause the elastomers to stiffen and become brittle. In addition, known elastomeric polymers, such as polysiloxanes, that are able to individually maintain flexibility at low temperatures may have reduced mechanical strength at low temperatures. Known elastomeric systems may exhibit dramatic stiffening at low temperatures due to onset of the glass transition temperature (Tg) from polymeric chains in the material. Below Tg, the elastomer may experience an abrupt increase in modulus of 10-100 times upon cooling, rendering the material hard and brittle. Many resins composed of silicones or polyurethanes which are commonly used on aircraft exterior surfaces may undergo this transition at −30° C. to −40° C. However, since the temperature at high altitudes is often well below this range, it is desirable to find an alternative that will maintain flexibility at lower temperatures.
Addition of particulate fillers in the range of 10-100 nm (nanometers) may have a beneficial effect on the mechanical properties of elastomers, and they are typically referred to as “reinforcing fillers”. However larger particles, such as in the 1-100 μm (micrometer) range, may have a detrimental effect on elastomer mechanical properties, yet these particles are often desirable in order to add additional functionality to the overall composite material. Moreover, while some elastomeric materials may possess lower Tgs, they may be incapable of being processed in solution mixed with high levels of solid fillers and easily applied over vehicle scale areas.
In addition, known systems and methods exist regarding the use of polyether compounds to improve the mechanical properties of segmented polyurea silioxanes. However, these materials use the polyether compounds as a second soft segment block to reside between the silicone and urea hard segments rather than as a chain extender or curative, thus producing a different chain backbone structure. Such an intermediate polyether segment introduces a structural element into the polymer system with a higher glass transition temperature (Tg) of approximately −50° C. that may reduce the low temperature range over which the material is elastic. Moreover, the addition of fillers to these materials is desirable.
Further, it is desirable for elastomeric materials to be able to be formulated into a form that may be conveniently prepared and applied in the field. This may require precursor components that are capable of being stored and stable over acceptable time periods. Once combined, the elastomeric precursors may demonstrate an acceptable pot life or be suspended in a medium that allows for convenient application. Low general toxicity of individual components, chemical resistance to fluids commonly found in aerospace environments, and the ability to be compounded with filler materials are also desirable.
Accordingly, there is a need for filled composite materials that can maintain classic elastic properties and continue to demonstrate high degrees of toughness in low temperature, demanding environments, as well as a need for flexible, low temperature, filled composite material compositions, coatings, and methods that provide advantages over known compositions, coatings, and methods.